In the broadest sense, we are interested in determining whether clock genes (Perl, Per2, Bmal, and Clk) are involved in hippocampal physiology and whether they impose a temporal structure to learning and memory functions. In order to test this general hypothesis, we propose to address a series of approachable questions: 1) Are clock genes rhythmically expressed in the HIP? 2) Are these rhythms restricted to certain cell populations within the HIP? 3) Does the induction of long term potentiation regulate the expression of these genes and does this regulation vary with a daily cycle? 4) Does membrane depolarization and calcium influx drive mPER expression in the HIP? We provide preliminary data indicating that our experimental hypotheses are likely to be confirmed. In addressing these questions, we hope to better understand the possible role of clock genes in synaptic plasticity as well as provide insights as to how the circadian system imposes a temporal structure to learned behaviors [unreadable] [unreadable]